Prohibit changes to index mode, source, and sort settings during restore (#115811)

The index.mode, source.mode, and index.sort.* settings cannot be 
modified during restore, as this may lead to data corruption or issues
retrieving _source. This change enforces a restriction on modifying 
these settings during restore. While a fine-grained check could permit
equivalent settings, it seems simpler and safer to reject restore
requests if any of these settings are specified.

Author: dnhatn

docs/changelog/115811.yaml

@@ -0,0 +1,5 @@
+pr: 115811
+summary: "Prohibit changes to index mode, source, and sort settings during restore"
+area: Logs
+type: bug
+issues: []

server/src/internalClusterTest/java/org/elasticsearch/snapshots/RestoreSnapshotIT.java

@@ -23,6 +23,7 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeUnit;
 import org.elasticsearch.core.TimeValue;
+import org.elasticsearch.index.IndexMode;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.indices.InvalidIndexNameException;
@@ -761,6 +762,68 @@ public void testChangeSettingsOnRestore() throws Exception {
         assertHitCount(client.prepareSearch("test-idx").setSize(0).setQuery(matchQuery("field1", "bar")), numdocs);
     }
 
+    public void testRestoreChangeIndexMode() {
+        Client client = client();
+        createRepository("test-repo", "fs");
+        String indexName = "test-idx";
+        assertAcked(client.admin().indices().prepareCreate(indexName).setSettings(Settings.builder().put(indexSettings())));
+        createSnapshot("test-repo", "test-snap", Collections.singletonList(indexName));
+        cluster().wipeIndices(indexName);
+        for (IndexMode mode : IndexMode.values()) {
+            var error = expectThrows(SnapshotRestoreException.class, () -> {
+                client.admin()
+                    .cluster()
+                    .prepareRestoreSnapshot(TEST_REQUEST_TIMEOUT, "test-repo", "test-snap")
+                    .setIndexSettings(Settings.builder().put("index.mode", mode.name()))
+                    .setWaitForCompletion(true)
+                    .get();
+            });
+            assertThat(error.getMessage(), containsString("cannot modify setting [index.mode] on restore"));
+        }
+    }
+
+    public void testRestoreChangeSyntheticSource() {
+        Client client = client();
+        createRepository("test-repo", "fs");
+        String indexName = "test-idx";
+        assertAcked(client.admin().indices().prepareCreate(indexName).setSettings(Settings.builder().put(indexSettings())));
+        createSnapshot("test-repo", "test-snap", Collections.singletonList(indexName));
+        cluster().wipeIndices(indexName);
+        var error = expectThrows(SnapshotRestoreException.class, () -> {
+            client.admin()
+                .cluster()
+                .prepareRestoreSnapshot(TEST_REQUEST_TIMEOUT, "test-repo", "test-snap")
+                .setIndexSettings(Settings.builder().put("index.mapping.source.mode", "synthetic"))
+                .setWaitForCompletion(true)
+                .get();
+        });
+        assertThat(error.getMessage(), containsString("cannot modify setting [index.mapping.source.mode] on restore"));
+    }
+
+    public void testRestoreChangeIndexSorts() {
+        Client client = client();
+        createRepository("test-repo", "fs");
+        String indexName = "test-idx";
+        assertAcked(
+            client.admin()
+                .indices()
+                .prepareCreate(indexName)
+                .setMapping("host.name", "type=keyword", "@timestamp", "type=date")
+                .setSettings(Settings.builder().put(indexSettings()).putList("index.sort.field", List.of("@timestamp", "host.name")))
+        );
+        createSnapshot("test-repo", "test-snap", Collections.singletonList(indexName));
+        cluster().wipeIndices(indexName);
+        var error = expectThrows(SnapshotRestoreException.class, () -> {
+            client.admin()
+                .cluster()
+                .prepareRestoreSnapshot(TEST_REQUEST_TIMEOUT, "test-repo", "test-snap")
+                .setIndexSettings(Settings.builder().putList("index.sort.field", List.of("host.name")))
+                .setWaitForCompletion(true)
+                .get();
+        });
+        assertThat(error.getMessage(), containsString("cannot modify setting [index.sort.field] on restore"));
+    }
+
     public void testRecreateBlocksOnRestore() throws Exception {
         Client client = client();
 

server/src/main/java/org/elasticsearch/snapshots/RestoreService.java

@@ -67,9 +67,11 @@
 import org.elasticsearch.core.Tuple;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexSettings;
+import org.elasticsearch.index.IndexSortConfig;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.Mapping;
+import org.elasticsearch.index.mapper.SourceFieldMapper;
 import org.elasticsearch.index.shard.IndexLongFieldRange;
 import org.elasticsearch.index.shard.IndexShard;
 import org.elasticsearch.index.shard.ShardId;
@@ -155,7 +157,13 @@ public final class RestoreService implements ClusterStateApplier {
         SETTING_VERSION_CREATED,
         SETTING_INDEX_UUID,
         SETTING_CREATION_DATE,
-        SETTING_HISTORY_UUID
+        SETTING_HISTORY_UUID,
+        IndexSettings.MODE.getKey(),
+        SourceFieldMapper.INDEX_MAPPER_SOURCE_MODE_SETTING.getKey(),
+        IndexSortConfig.INDEX_SORT_FIELD_SETTING.getKey(),
+        IndexSortConfig.INDEX_SORT_ORDER_SETTING.getKey(),
+        IndexSortConfig.INDEX_SORT_MODE_SETTING.getKey(),
+        IndexSortConfig.INDEX_SORT_MISSING_SETTING.getKey()
     );
 
     // It's OK to change some settings, but we shouldn't allow simply removing them